In order to study different classes of DNA lesions, we have purified enz Studies in this laboratory are designed to elucidate the role of DNA repair processes in carcinogenesis and in neurodegeneration. We had previously obtained evidence that Alzheimer disease cells have defective nucleotide excision repair of DNA damaged by free radicals. This research grew out of work on xeroderma pigmentosum, an inherited disease in which cells are unable to conduct nucleotide excision repair of damaged DNA. As a result of this inability, patients with xeroderma pigmentosum are at a very high risk of developing sunlight-induced skin cancers, and some patients also experience degeneration of the nervous system which results from the patients' inability to repair free radical-induced damage to their neuronal DNA. We are developing new assays to confirm the presence of defective DNA repair in Alzheimer disease cells and in cells from cancer-prone diseases by an easily understood, automated assay that can readily be used in any laboratory capable of culturing human skin fibroblasts. We hope to elucidate the specific free radical-induced lesion(s) which Alzheimer disease and xeroderma pigmentosum cells cannot repair. To accomplish these goals, we have developed methods to place certain types of DNA damage into plasmids and into DNA oligonucleotides, and we are able to test the cells for their ability to repair the damage. Some of our tests specifically measure nucleotide excision repair; others measure a different DNA repair process known as base excision repair. We are using whole-cell and nuclear extracts from the adult rat brain to measure the capability of mammalian cells to perform nucleotide- and base-excision DNA repair. The use of these assays is expected to enable us to identify and study the DNA-repair defects in Alzheimer disease and in diseases with an increased incidence of cancer.